Method of alloying titanium



Aug. 20, 1963 Un aens e Filed Jan. 28, 1959 0f Rel/eff H'qper' d' P f5 Overs/3e I Prqper @173e Pelle fs Cold 7770/6/ for 27o Over-.ege rc Furnace INVENTOR.`

LLTLTL United States Patent f 3,101,267 METHOD F ALLOYING TITANIUM Edward I. Dunn, 4 Warner Lane, Thomaston, Conn. Filed Jan. 28, 1959, Ser. No. 789,758

1 Claim. (Cl. 75-10) (Granted under riitle 35, U.S. Code (1952), sec. 266) 'Ihe invention described herein may be manufactured and/or used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

This invention relates to the production of titanium alloys and is particularly directed to an improved method for obtaining such alloys. In the art of titanium alloy melting it has generally been found necessary to double melt in order to obtain the desired structural uniformity and compositional homogeneity. In this double melt process, titanium sponge and the desired alloy additions are physically mixed and fed into a cold mold arc furnace where they are melted and solidified into an ingot. The ingot obtained from this first melting is of such poor uniformity, as the result of inherently poor premixing and the shallow molten metal pool in this type of melting, that it is entirely unsuitable for fabrication into finished products. Instead, the ingot becomes the consumahle electrode in a larger cold ymold arc furnace where it is remelted into a more homogeneous ingot which is suitable for fabrication.

Since this rather cumbersome and `expensive process is due in large measure to the poor uniformity obtained in premixing, it would appear that great advantage might be derived from improving the character of the mixture first subjected to the arc. In U.S. vPatent No. 2,855,331, issued October 7, 1958, there is `disclosed a method for obtaining titanium metal of high purity. Briefly stated, the method involves deposition of titanium halide on metallic particles maintained at Ia temperature above the decomposition temperature of the titanium halide. In the process for obtaining titanium :alloys which is the subject of the present invention, the halide decomposition method for obtaining titanium metal will be employed. This halide decomposition method yields a solid, dense deposit of titanium metal, rather than a porous deposit as in the sponge (Kroll) process. While the signhicance of the fact will be more fully explored in the subsequent discussion, it should be noted at this point that since the titanium deposit is relatively dense and uniform in this process, there is close correlation between the volume of the titanium deposit and its Weight.

It is an 'object of this invention to simplify the production of titanium alloys.

It is another object of this invention to utilize the thermal decomposition of titanium halides in a method for producing titanium alloys.

It is a further object of this invention to utilize an improved physical mixture of titanium and additives to reduce the number of melting steps required to produce titanium alloy ingots.

It is still another object of this invention to closely control the composition of a titanium alloy melt by controlling the composition of the mechanical mixture charged into the furnace.

Still another object of this invention is the provision of a method for melting and casting titanium alloys which is easily adapted to continuous operation.

Other objects and advantages of the invention will become apparent in the course of the description which follows.

In the drawing, which forms a part of this description, the FIGURE is a ilow sheet illustrating the method of this invention.

The process as shown in the ligure includes the following principal steps in the order listed:

(1) Pelletizng.-'I'his is the production .of seed particlesor 'pellets for use in a later deposition step.

The pellets are composed of the alloying materials or additives desired in the linal titanium base` alloy. 'I'he manner in which the additive pellets are produced depends to a large degree upon the physical properties of the additive. Those metals which are ductile can be pelletized in a shot tower. Brittle metals can be reduced to pellets Iby a crushing process.

(2) First screening-This step is calculated to Obtain pellets of a predetermined weight by size screening. At least two screens are used, and pellets which pass through a iirst screen element but are retained on a second screen element are of the proper uniform size (Weight). Both undersize and oversize pellets lare removed from the process at this point, but, with proper adjustment of the processing equipment they may be run through the balance of the process at a later time.

(3) Titanium dep0sz`tion.-In this step the alloy pellets receive a titanium coating of predetermined weight. The additive pellets of proper size are introduced into a dissociating furnace in which there is maintained an atmosphere of a titanium halide, preferably titanium tetraiodide. In the dissociating furnace the pellets are heated to a temperature of approximately l200 C., at which temperature the halide dissociates, depositing titanium on the alloy pellets. The amount of titanium deposited on the pellets, so long as the temperature is maintained at l200 C. and a llow of titanium halide through the furnace is established, depends only upon the time the pellets remain in the furnace. It is contemplated that the time :of operation of the dissociating furnace will be so adjusted that oversize pellets will not be produced. `When the pellets have grown to some predetermined size-they are removm from the furnace for further processing.

(4) Second screening-The tri-metallic pellets having the proper titanium-to-alloy weight ratio are in this step segregated from the undersize pellets. The undersize pellets can later be recirculated through the deposition equipment. As previously pointed out, the titanium deposit obtained is dense and uniform and therefore, titanium deposits having similar volumes will have very nearly the same weight. Since the seed or additive pellets are ,of nearly the same weight, it may be said that the tri-metallic pellets have the same titanium-to-alloy weight ratio. lust what that ratio is, of course, depends upon the screens used.

(5) Melting-The tri-metallic pellets having the proper titanium-to-alloy ratio are melted and cast into titanium alloy ingots. This step is ordinarily carried out in the conventional cold mold arc furnace.

-It should be understood that the undersize and oversize pelllets obtained in step 2 of this process could be run through steps 3-5 in separate batches. The time in the dissociating furnace would be shorter for the undersize pellets and longer for the oversize pellets. Screens of appropriate size would be used in step 4 tol secure pellets having the proper titanium-to-alloy weight ratio.

A dissociating furnace suitable for the practice of this invention is disclosed in U.S. Patent No. 2,855,331. In that furnace the pellets are kept in continuous motion by rotating the furnace while the moving pellets are inductively heated to the proper temperature by a coil surrounding the furnace. Automatic removal and screening of the bi-metallic pellets can be effected by employing the inclined rotary dissociating furnace also shown in U.S. Patent No. 2,855,331.

The tri-metallic pellets of titanium and alloy metal have very large surface areas at which the two constituents of the pellet are in intimate contact with each other.

Patented Aug. 20, 1963.

of titanium can be made.

vThis isa condition most favorable for rapid and uniform Y intermixture upon melting, with minimum loss of additives. TIhis intimate and uniform mixture obtained in this manne-r cannotbe approached by conventional mechanical mixing techniques.

As exampieof ,the product of this process, if van alloy of titanium and chromium is desired, relatively f oci thepellet (as determined by the second screening) was titanium. Since each chromium pellet -is surrounded by the proper amount of titanium and theY metals have rel-atively large surface areas in contact with each other the mixture'may be characterized as both uniform and intirri-ate.v Upon melting a charge of these bi-rnetallic pellets in thev usual cold mold arc furnace, a 95% Ti-5% Cr alloy having ahi'gh degree fofkuniformity results.

By using va bi-metallic pellet as seed. a ternary alloy The two alloying metals are premelted'fin the correct proportions and cast as small shot'. rThese pellets arev then fed into the' dissociation Y furnace upon which the much larger quantity of titanium Since lthese binaries are brittle, the binaryv Quaternaries, quintaries, etc. can be produced by the same general method.

a novel method incorporating the advantages stated in Ithe above description. It is to be understood that the invention is susceptible of various modications without departing from the spirit or scope of the invention.

What is claimed is:

A method for producing alloys of titaniumcomprising thesteps of pelletizing the additives, screening the additive pellets to obtain pellets of a uniform size and com,- position, heating said pellets to a halide decomposing temperature in a titanium halide atmosphere to deposit titanium metal thereon, screening the composite pellets to obtain pellets of la selected'size and composition,Vv and meltingrsai-d composite pellets of said selected size andv to obtain the composition, in a Vcold mold are' furnace desired titanium alloy.

References C ited in the le ofpthis patent Y UNITED STATES PATENTS 

